Request routing utilizing client location information

ABSTRACT

A system, method, and computer-readable medium for request routing based on client location information are provided. A content delivery network service provider receives a DNS query from a client computing device. The DNS query corresponds to a resource identifier for requested content from the client computing device. The content delivery network service provider transmits an alternative resource identifier in response to the client computing device DNS query. The alternative resource identifier is selected as a function of client location information. The client location information is obtained from information corresponding to a mapping of at least partial IP addresses to known locations. The client computing device then issues a second DNS query to the same content delivery network service provider. The content delivery network service provider can then either resolve the second DNS query with an IP address of a cache component or transmit another alternative resource identifier that will resolve to the content delivery network service provider. The process can repeat with the content delivery network service provider&#39;s network until a DNS server resolves a DNS query from the client computing device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 11/771,679,filed on Jun. 29, 2007, and entitled “Mapping Attributes to NetworkAddresses,” which is herein incorporated by reference.

BACKGROUND

Generally described, computing devices and communication networks can beutilized to exchange information. In a common application, a computingdevice can request content from another computing device via thecommunication network. For example, a user at a personal computingdevice can utilize a software browser application to request a Web pagefrom a server computing device via the Internet. In such embodiments,the user computing device can be referred to as a client computingdevice and the server computing device can be referred to as a contentprovider.

Content providers are generally motivated to provide requested contentto client computing devices often with consideration of efficienttransmission of the requested content to the client computing deviceand/or consideration of a cost associated with the transmission of thecontent. For larger scale implementations, a content provider mayreceive content requests from a high volume of client computing deviceswhich can place a strain on the content provider's computing resources.Additionally, the content requested by the client computing devices mayhave a number of components, which can further place additional strainon the content provider's computing resources.

With reference to an illustrative example, a requested Web page, ororiginal content, may be associated with a number of additionalresources, such as images or videos, which are to be displayed with theWeb page. In one specific embodiment, the additional resources of theWeb page are identified by a number of embedded resource identifiers,such as uniform resource locators (“URLs”). In turn, software on theclient computing devices typically processes embedded resourceidentifiers to generate requests for the content. Often, the resourceidentifiers associated with the embedded resources reference a computingdevice associated with the content provider such that the clientcomputing device would transmit the request for the additional resourcesto the referenced content provider computing device. Accordingly, inorder to satisfy a content request, the content provider would provideclient computing devices data associated with the Web page as well asthe data associated with the embedded resources.

Some content providers attempt to facilitate the delivery of requestedcontent, such as Web pages and/or resources identified in Web pages,through the utilization of a content delivery network (“CDN”) serviceprovider. A CDN server provider typically maintains a number ofcomputing devices in a communication network that can maintain contentfrom various content providers. In turn, content providers can instruct,or otherwise suggest to, client computing devices to request some, orall, of the content provider's content from the CDN service provider'scomputing devices.

As with content providers, CDN service providers are also generallymotivated to provide requested content to client computing devices oftenwith consideration of efficient transmission of the requested content tothe client computing device and/or consideration of a cost associatedwith the transmission of the content. Accordingly, CDN service providersoften consider factors such as latency of delivery of requested contentin order to meet service level agreements or to generally improve thequality of delivery service.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrative of content delivery environmentincluding a number of client computing devices, a content provider, anda content delivery network service provider;

FIG. 2 is a block diagram of the content delivery environment of FIG. 1illustrating the registration of a content provider with a contentdelivery service provider;

FIG. 3 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of a content request from aclient computing device to a content provider;

FIGS. 4A-4B are block diagrams of the content delivery environment ofFIG. 1 illustrating one embodiment of the generation and processing of aDNS query corresponding to an embedded resource from a client computingdevice to a content delivery network service provider and the subsequentgeneration and processing of DNS queries corresponding to a firstalternative resource identifier from a client computing device to acontent delivery network;

FIG. 5 is a block diagram of the content delivery environment of FIG. 1illustrating another embodiment of the generation and processing of aDNS query corresponding to an embedded resource from a client computingdevice to a content delivery network service provider;

FIG. 6 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of embedded resource requestsfrom a client computing device to a content delivery network serviceprovider;

FIG. 7 is a flow diagram illustrative of a request routing routineimplemented by a content delivery network service provider utilizingquery IP address to location-based identifier mappings to process aresource request; and

FIG. 8 is a flow diagram illustrative a request routing subroutineimplemented by a content delivery network service provider in theillustrative flow diagram of FIG. 7 for determining a network point ofpresence for servicing a resource request based on an obtainedlocation-based identifier.

DETAILED DESCRIPTION

Generally described, the present disclosure is directed to routing ofDNS queries from a client computing device corresponding to contentrequests by a network resource, such as content delivery network (“CDN”)service providers. The processing of a DNS query by a CDN serviceprovider is generally referred to as request routing. Specifically,aspects of the disclosure will be described with regard to the routingof a client computing device DNS query within a content delivery networkservice provider domain as a function of client location informationassociated with the processing of the content request from the clientcomputing device. In one embodiment, a CDN service provider utilizesquery IP address to location-based identifier mappings to selectcomponents of a CDN network to provide the requested resource. The CDNnetwork component can be selected by identifying a client computingdevice's location and attempting to improve performance associated withthe request routing by transmitting requested resources from a CDNnetwork component in a destination associated with the client'slocation. Although various aspects of the disclosure will be describedwith regard to illustrative examples and embodiments, one skilled in theart will appreciate that the disclosed embodiments and examples shouldnot be construed as limiting.

FIG. 1 is a block diagram illustrative of content delivery environment100 for the management and processing of content requests. Asillustrated in FIG. 1, the content delivery environment 100 includes anumber of client computing devices 102 (generally referred to asclients) for requesting content from a content provider and/or a CDNservice provider. In an illustrative embodiment, the client computingdevices 102 can correspond to a wide variety of computing devicesincluding personal computing devices, laptop computing devices,hand-held computing devices, terminal computing devices, mobile devices,wireless devices, various electronic devices and appliances and thelike. In an illustrative embodiment, the client computing devices 102include necessary hardware and software components for establishingcommunications over a communication network 108, such as a wide areanetwork or local area network. For example, the client computing devices102 may be equipped with networking equipment and browser softwareapplications that facilitate communications via the Internet or anintranet.

Although not illustrated in FIG. 1, each client computing device 102utilizes some type of local DNS resolver component, such as a DNS nameserver, that generates the DNS queries attributed to the clientcomputing device. In one embodiment, the local DNS resolver componentmay be provided by an enterprise network to which the client computingdevice 102 belongs. In another embodiment, the local DNS resolvercomponent may be provided by an Internet Service Provider (ISP) thatprovides the communication network connection to the client computingdevice 102.

The content delivery environment 100 can also include a content provider104 in communication with the one or more client computing devices 102via the communication network 108. The content provider 104 illustratedin FIG. 1 corresponds to a logical association of one or more computingdevices associated with a content provider. Specifically, the contentprovider 104 can include a web server component 110 corresponding to oneor more server computing devices for obtaining and processing requestsfor content (such as Web pages) from the client computing devices 102.The content provider 104 can further include an origin server component112 and associated storage component 114 corresponding to one or morecomputing devices for obtaining and processing requests for networkresources from the CDN service provider. One skilled in the relevant artwill appreciate that the content provider 104 can be associated withvarious additional computing resources, such additional computingdevices for administration of content and resources, DNS name servers,and the like. For example, although not illustrated in FIG. 1, thecontent provider 104 can be associated with one or more DNS name servercomponents that are operative to receive DNS queries related toregistered domain names associated with the content provider. The one ormore DNS name servers can be authoritative to resolve client computingdevice DNS queries corresponding to the registered domain names of thecontent provider 104. A DNS name server component is considered to beauthoritative to a DNS query if the DNS name server can resolve thequery by providing a responsive IP address.

With continued reference to FIG. 1, the content delivery environment 100can further include a CDN service provider 106 in communication with theone or more client computing devices 102 and the content providers 104via the communication network 108. The CDN service provider 106illustrated in FIG. 1 corresponds to a logical association of one ormore computing devices associated with a CDN service provider.Specifically, the CDN service provider 106 can include a number of Pointof Presence (“POP”) locations 116, 122, 128 that correspond to nodes onthe communication network 108. Each POP 116, 122, 128 includes a DNScomponent 118, 124, 130 made up of a number of DNS server computingdevices for resolving DNS queries from the client computers 102. EachPOP 116, 122, 128 also includes a resource cache component 120, 126, 132made up of a number of cache server computing devices for storingresources from content providers and transmitting various requestedresources to various client computers.

Still further, the CDN service provider 106 includes a routing datastore 134 for maintaining information regarding query IP address tolocation-based identifier mappings, as well as confidence factorsassociated with those mappings, such as disclosed in U.S. applicationSer. No. 11/771,679, which is herein incorporated by reference. In someembodiments, the location-based identifiers can correspond to locationsdirectly determined based on physical locations or logical locationsassociated with the origin of the DNS query. In addition oralternatively, the location-based identifier can be inferred based onassociating a relative location to known locations. For example, thelocation-based identifier can be attributed to known locations of POPs(corresponding to the CDN service provider) based on measured latencyinformation associated with request routing between the client computingdevice or its local DNS resolver and these POPs. The measured latencyinformation can be premeasured, such as through testing procedures orpreviously observed request routing behavior. Alternatively, themeasured latency information can be dynamically measured in a real timebasis or semi-real time basis.

The routing data store 134 can also maintain additional location mappinginformation such as mappings of the location-based identifiers toregional CDN destination identifiers. Even further, the location mappingdata store 134 can include information identifying a set of POPsassociated with each CDN destination identifier. Yet further, therouting data store 134 can include user profile information from whichalternative user location information may be obtained. Yet stillfurther, the routing data store 134 can include content provider routingcriteria associated with a content provider identifier (or originidentifier), such as regional service plan information or other routingcriteria, utilized by the CDN service provider 106 to route contentrequests.

In an illustrative embodiment, the routing data store 134 corresponds toa central data store accessible by the POPs 116, 122, 128, such as via aWeb service. In another embodiment, each POP 116, 122, 128 can maintaina local version of a routing data store 134 for utilization in requestrouting as will be explained in greater detail. Additionally, althoughthe routing data store 134 is illustrated as a single data store, oneskilled in the relevant art will appreciate that routing data store 134may correspond to one or more data stores and may be implemented in adistributed manner.

The DNS components 118, 124 and 130 and the resource cache components120, 126 132 may further include additional software and/or hardwarecomponents that facilitate communications including, but not limited,load balancing or load sharing software/hardware components.

In an illustrative embodiment, the DNS component 118, 124, 130 andresource cache component 120, 126, 132 are considered to be logicallygrouped, regardless of whether the components, or portions of thecomponents, are physically separate. Additionally, although the POPs116, 122, 128 are illustrated in FIG. 1 as logically associated with theCDN service provider 106, the POPs will be geographically distributedthroughout the communication network 108 in a manner to best servevarious demographics of client computing devices 102. Additionally, oneskilled in the relevant art will appreciate that the CDN serviceprovider 106 can be associated with various additional computingresources, such additional computing devices for administration ofcontent and resources, and the like.

One skilled in the relevant art will appreciate that the components andconfigurations provided in FIG. 1 are illustrative in nature.Accordingly, additional or alternative components and/or configurations,especially regarding the additional components, systems and subsystemsfor facilitating communications may be utilized.

With reference now to FIGS. 2-6, the interaction between variouscomponents of the content delivery environment 100 of FIG. 1 will beillustrated. For purposes of the example, however, the illustration hasbeen simplified such that many of the components utilized to facilitatecommunications are not shown. One skilled in the relevant art willappreciate that such components can be utilized and that additionalinteractions would accordingly occur without departing from the spiritand scope of the present disclosure.

With reference to FIG. 2, an illustrative interaction for registrationof a content provider 104 with the CDN service provider 106 will bedescribed. As illustrated in FIG. 2, the CDN content registrationprocess begins with registration of the content provider 104 with theCDN service provider 106. In an illustrative embodiment, the contentprovider 104 utilizes a registration application program interface(“API”) to register with the CDN service provider 106 such that the CDNservice provider 106 can provide content on behalf of the contentprovider 104. The registration API includes the identification of theorigin server 112 of the content provider 104 that will providerequested resources to the CDN service provider 106. Additionally, aswill be explained in greater detail below, the content provider 104 canalso provide additional information, such as regional service planinformation or other routing criteria, utilized by the CDN serviceprovider 106 to route content requests. In one embodiment, the routingcriteria can include the specification of a particular regional serviceplan, which may limit the regions from which content requests may beresolved by the CDN service provider 106. In another embodiment, therouting criteria can include a selection by the content provider 104that the CDN service provider 106 should attempt to service specificresource requests from a particular regional destination or POP or froma particular distribution of regional destinations or POPs.

One skilled in the relevant art will appreciate that upon identificationof appropriate origin servers 112, the content provider 104 can begin todirect requests for content from client computing devices 102 to the CDNservice provider 106. Specifically, in accordance with DNS routingprinciples, a client computing device request corresponding to aresource identifier would eventually be directed toward a POP 116, 122,128 associated with the CDN service provider 106. In the event that theresource cache component 120, 126, 132 of a selected POP does not have acopy of a resource requested by a client computing device 102, theresource cache component will request the resource from the originserver 112 previously registered by the content provider 104.

With continued reference to FIG. 2, upon receiving the registration API,the CDN service provider 106 obtains and processes the registrationinformation. In an illustrative embodiment, the CDN service provider 106can then generate additional information that will be used by the clientcomputing devices 102 as part of the content requests. The additionalinformation can include, without limitation, content provideridentifiers, such as content provider identification codes or originserver identifiers, executable code for processing resource identifiers,such as script-based instructions, and the like. One skilled in therelevant art will appreciate that various types of additionalinformation may be generated by the CDN service provider 106 and thatthe additional information may be embodied in any one of a variety offormats.

The CDN service provider 106 returns an identification of applicabledomains for the CDN service provider (unless it has been previouslyprovided) and any additional information to the content provider 104. Inturn, the content provider 104 can then process the stored content withcontent provider specific information. In one example, as illustrated inFIG. 2, the content provider 104 translates resource identifiersoriginally directed toward a domain of the origin server 112 to a domaincorresponding to the CDN service provider. The translated URLs areembedded into requested content in a manner such that DNS queries forthe translated URLs will resolve to a DNS server corresponding to theCDN service provider 106 and not a DNS server corresponding to thecontent provider 104. Although the translation process is illustrated inFIG. 2, in some embodiments, the translation process may be omitted in amanner described in greater detail below.

Generally, the identification of the resources originally directed tothe content provider 104 will be in the form of a resource identifierthat can be processed by the client computing device 102, such asthrough a browser software application. In an illustrative embodiment,the resource identifiers can be in the form of a uniform resourcelocator (“URL”). Because the resource identifiers are included in therequested content directed to the content provider, the resourceidentifiers can be referred to generally as the “content provider URL.”For purposes of an illustrative example, the content provider URL canidentify a domain of the content provider 104 (e.g.,contentprovider.com), a name of the resource to be requested (e.g.,“resource.xxx”) and a path where the resource will be found (e.g.,“path”). In this illustrative example, the content provider URL has theform of:

-   -   http://www.contentprovider.com/path/resource.xxx

During an illustrative translation process, the content provider URL ismodified such that requests for the resources associated with thetranslated URLs resolve to a POP associated with the CDN serviceprovider 106. In one embodiment, the translated URL identifies thedomain of the CDN service provider 106 (e.g., “cdnprovider.com”), thesame name of the resource to be requested (e.g., “resource.xxx”) and thesame path where the resource will be found (e.g., “path”). Additionally,the translated URL can include additional processing information (e.g.,“additional information”). Specifically, as set forth above, in oneillustrative embodiment, the additional information can include acontent provider identifier. Additionally, the translated URL caninclude any additional information utilized by the CDN service providerduring the request routing information, including, but not limited to,service plan information, file identifiers, and the like. Suchinformation may be included in the modified URL or may be omitted fromthe translated URL and obtained by the CDN service provider 106 duringthe request routing process, such as by a lookup according to a contentprovider identifier. The translated URL would have the form of:

-   -   http://additional_information.cdnprovider.com/path/resource.xxx

In another embodiment, the information associated with the CDN serviceprovider 106 is included in the modified URL, such as through prependingor other techniques, such that the translated URL can maintain all ofthe information associated with the original URL. In this embodiment,the translated URL would have the form of:

-   -   http://additional_information.cdnprovider.com/www.contentprovider.com/path/resource.xxx

With reference now to FIG. 3, after completion of the registration andtranslation processes illustrated in FIG. 2, a client computing device102 subsequently generates a content request that is received andprocessed by the content provider 104, such as through the Web server110. In accordance with an illustrative embodiment, the request forcontent can be in accordance with common network protocols, such as thehypertext transfer protocol (“HTTP”). Upon receipt of the contentrequest, the content provider 104 identifies the appropriate responsivecontent. In an illustrative embodiment, the requested content cancorrespond to a Web page that is displayed on the client computingdevice 102 via the processing of information, such as hypertext markuplanguage (“HTML”), extensible markup language (“XML”), and the like. Therequested content can also include a number of embedded resourceidentifiers, described above, that corresponds to resource objects thatshould be obtained by the client computing device 102 as part of theprocessing of the requested content. The embedded resource identifierscan be generally referred to as original resource identifiers ororiginal URLs.

Upon receipt of the requested content, the client computing device 102,such as through a browser software application, begins processing any ofthe markup code included in the content and attempts to acquire theresources identified by the embedded resource identifiers. Accordingly,the first step in acquiring the content corresponds to the issuance, bythe client computing device 102 (through its local DNS resolver), of aDNS query for the original URL resource identifier that results in theidentification of a DNS server authoritative to the “.” and the “com”portions of the translated URL. After processing the “.” and “com”portions of the embedded URL, the client computing device 102 thenissues a DNS query for the resource URL that results in theidentification of a DNS server authoritative to the “.cdnprovider”portion of the embedded URL. The issuance of DNS queries correspondingto the “.” and the “com” portions of a URL are well known and have notbeen illustrated.

With reference now to FIGS. 4A, in an illustrative embodiment, thesuccessful resolution of the “cdnprovider” portion of the original URLidentifies a network address, such as an IP address, of a DNS serverassociated with the CDN service provider 106. In one embodiment, the IPaddress can be a specific network address unique to a DNS servercomponent of a POP. In another embodiment, the IP address can be sharedby one or more POPs. In this embodiment, a further DNS query to theshared IP address utilizes a one-to-many network routing schema, such asanycast, such that a specific POP will receive the request as a functionof network topology. For example, in an anycast implementation, a DNSquery issued by a client computing device 102 to a shared IP addresswill arrive at a DNS server component logically having the shortestnetwork topology distance, often referred to as network hops, from theclient computing device. The network topology distance does notnecessarily correspond to geographic distance. However, in someembodiments, the network topology distance can be inferred to be theshortest network distance between a client computing device 102 and aPOP.

With continued reference to FIG. 4A, in either of the above identifiedembodiments (or any other embodiment), a specific DNS server in the DNScomponent 118 of a POP 116 receives the DNS query corresponding to theoriginal URL from the client computing device 102. Once one of the DNSservers in the DNS component 118 receives the request, the specific DNSserver attempts to resolve the request. In one illustrative embodiment,as shown in reference to FIG. 5, a specific DNS server resolves the DNSquery by identifying an IP address of a cache server component that willprocess the request for the requested resource. As described above andas will be described further below in reference to FIG. 6, a selectedresource cache component can process the request by either providing therequested resource if it is available or attempt to obtain the requestedresource from another source, such as a peer cache server computingdevice or the origin server 112 of the content provider 104.

Returning to FIG. 4A, as an alternative to selecting a resource cachecomponent upon receipt of a DNS query as described in reference to FIG.5, the CDN service provider 106 can maintain sets of various alternativeresource identifiers. The alternative resource identifiers can beprovided by the CDN service provider 106 to the client computing device102 such that a subsequent DNS query on the alternative resourceidentifier will be processed by a different DNS server component withinthe CDN service provider's network. In an illustrative embodiment, thealternative resource identifiers are in the form of one or morecanonical name (“CNAME”) records. In one embodiment, each CNAME recordidentifies a domain of the CDN service provider 106 (e.g.,“cdnprovider.com” or “cdnprovider-1.com”). As will be explained ingreater detail below, the domain in the CNAME does not need to be thesame domain found in original URL or in a previous CNAME record.Additionally, each CNAME record includes additional information, such asrequest routing information, (e.g., “request routing information”). Anillustrative CNAME record can have the form of:

-   -   http://request_routing_information.cdnprovider.com/path/resource.xxx        CNAMErequest_routing_information.cdnprovider.com

In an illustrative embodiment, the CNAME records are generated andprovided by the DNS servers to identify a more appropriate DNS server ofthe CDN service provider 106. As used in accordance with the presentdisclosure, appropriateness can be defined in any manner by the CDNservice provider 106 for a variety of purposes. In an illustrativeembodiment, as will be described in greater detail below in reference toFIGS. 7 and 8, the CDN service provider 106 will utilize client locationinformation associated with the client computing device 102 or its localDNS resolver, at least in part, to identify the more appropriate DNSserver of the CDN service provider 106. In particular, the CDN serviceprovider 106 can utilize an IP address associated with a clientcomputing device DNS query to identify a corresponding location-basedidentifier representing a possible location of the client computingdevice. The CDN service provider 106 can then, in turn, utilize thelocation-based identifier to identify a destination identifierrepresenting a geographic region associated with the CDN serviceprovider 106 from which the resource request should be resolved. Basedon the destination identifier, the CDN service provider 106 can thenselect a POP 116, 122, 128 from a set of POPs that are capable ofservicing resource requests for the destination corresponding to thedestination identifier. In one example, if more than one POP isidentified in the set, the CDN service provider 106 can utilize adistribution allocation for selecting a specific POP associated with theidentified destination. In another example, once a POP is selected, theCDN service provider 106 can further use health information to determinewhether the selected POP is available to service requests beforeproviding the client computing device with a CNAME corresponding to theselected POP. One skilled in the art will appreciate that the abovefunctionality is illustrative in nature and accordingly should not beconstrued as limiting.

As described above, in addition to the consideration of client locationinformation (either of the end-client or its associated local DNSresolver component), the CDN service provider 106 can utilize theadditional information (e.g., the “additional information”) included inthe translated URL to select a more appropriate DNS server. In oneaspect, the CDN service provider 106 can utilize the additionalinformation to select from a set of DNS servers identified as satisfyingcriteria associated with the client location information. In anotheraspect, the CDN service provider 106 can utilize the additionalinformation to validate the DNS server selected in accordance with theclient location information or to select an alternative DNS serverpreviously selected in accordance with the client location information.In one example, the CDN service provider 106 can attempt to direct a DNSquery to DNS servers according to additional geographic criteria. Theadditional geographic criteria can correspond to geographic-basedregional service plans contracted between the CDN service-provider 106and the content provider 104 in which various CDN service provider 106POPs are grouped into geographic regions. Accordingly, a clientcomputing device 102 DNS query received in a region not corresponding tothe content provider's regional plan may be better processed by a DNSserver in region corresponding to the content provider's regional plan.

In another example, the CDN service provider 106 can attempt to direct aDNS query to DNS servers according to service level criteria. Theservice level criteria can correspond to service or performance metricscontracted between the CDN service provider 106 and the content provider104. Examples of performance metrics can include latencies of datatransmission between the CDN service provider POPs and the clientcomputing devices 102, total data provided on behalf of the contentprovider 104 by the CDN service provider POPs, error rates for datatransmissions, and the like.

In still a further example, the CDN service provider 106 can attempt todirect a DNS query to DNS servers according to network performancecriteria. The network performance criteria can correspond tomeasurements of network performance for transmitting data from the CDNservice provider POPs to the client computing device 102. Examples ofnetwork performance metrics can include network data transfer latencies(measured by the client computing device or the CDN service provider106, network data error rates, and the like.

In accordance with an illustrative embodiment, the DNS server maintainsa data store that defines CNAME records for various original URLs. If aDNS query corresponding to a particular original URL matches an entry inthe data store, the DNS server returns a CNAME record as defined in thedata store. In an illustrative embodiment, the data store can includemultiple CNAME records corresponding to a particular original URL. Themultiple CNAME records would define a set of potential candidates thatcan be returned to the client computing device. In such an embodiment,the DNS server, either directly or via a network-based service, canimplement additional logic in selecting an appropriate CNAME from a setof possible of CNAMEs. In an illustrative embodiment, each DNS servercomponent 118, 124, 130 maintains the same data stores that define CNAMErecords, which can be managed centrally by the CDN service provider 106.Alternatively, each DNS server component 118, 124, 130 can have POPspecific data stores that define CNAME records, which can be managedcentrally by the CDN service provider 106 or locally at the POP 116,122, 128. Still further, each DNS server computing device within the DNSserver components 118, 124, 130 can utilize shared data stores managedby a respective POP or a local data store specific to an individual DNSserver computing device.

The returned CNAME can also include request routing information that isdifferent from or in addition to the information provided in theURL/CNAME of the current DNS query. For example, a specific regionalplan can be identified in the “request_routing_information” portion ofthe specific CNAME record. A similar approach could be taken to identifyservice level plans and file management by including a specificidentifier in the “request routing information” portion of the CNAMErecord. In another embodiment, request routing information can be foundin the identification of a CDN service provider 106 domain differentfrom the domain found in the current URL/CNAME. For example, a specificregional plan domain (e.g., “cdnprovder-region1.com”) could be used inthe domain name portion of the specific CNAME record. Any additionalrequest routing information can be prepended to the existing requestrouting information in the current URL/CNAME such that the previousrequest routing information would not be lost (e.g.,serviceplan.regionalplan.cdnprovider.com). One skilled in the relevantart will appreciate that additional or alternative techniques and/orcombination of techniques may be used to include the additional requestrouting information in the CNAME record that is selected by the DNSserver component 118.

With continued reference to FIG. 4A, one skilled in the relevant artwill appreciate that the DNS server may select (or otherwise obtain) aCNAME record that is intended to resolve to a more appropriate DNSserver of the CDN service provider 106. It may be possible, however,that the same DNS server would also be authoritative for the subsequentDNS query for the CNAME to be provided to the client computing device.For example, a specific DNS server may be authoritative based on theclient location information. Thus, returning a CNAME would still resultin the DNS query arriving at the same DNS server (which may also be duein part to the client computing device's geography). In such anembodiment, the DNS server, such as DNS server component 118, may chooseto resolve the future DNS query in advance.

With reference now to FIG. 4B, upon receipt of the CNAME from the DNSserver component 118, the client computing device 102 generates asubsequent DNS query corresponding to the CNAME. As previously discussedwith regard to FIG. 4A, the DNS query process could first start with DNSqueries for the “.” and “com” portions, followed by a query for the“cdnprovider” portion of the CNAME. To the extent, however, that theresults of a previous DNS queries can be cached (and remain valid), theclient computing device 102 can utilize the cached information and doesnot need to repeat the entire process. However, at some point, dependingon whether the CNAME provided by DNS server component 118 (FIG. 4A) andthe previous URL/CNAME share common CDN service provider domains, thecurrent CNAME DNS query will be processed by a different POP provided bythe CDN service provider 106. As illustrated in FIG. 4B, the DNS servercomponent 124 of POP 122 receives the current CNAME based on thedifferent information in the current CNAME previously provided by theDNS server component 118. As previously described, the DNS servercomponent 124 can then determine whether to resolve the DNS query on theCNAME with an IP address of a cache component that will process thecontent request or whether to provide another alternative resourceidentifier selected in the manners described above.

For purposes of illustration, assume that the DNS server component 124processes the content request by returning an IP address of a resourcecache component. In an illustrative embodiment, the DNS server component124 can utilize a variety of information in selecting a resource cachecomponent. In one example, the DNS server component 124 can default to aselection of a resource cache component of the same POP. In anotherexample, the DNS server components can select a resource cache componentbased on various load balancing or load sharing algorithms. Stillfurther, the DNS server components can utilize network performancemetrics or measurements to assign specific resource cache components.The IP address selected by a DNS server component may correspond to aspecific caching server in the resource cache. Alternatively, the IPaddress can correspond to a hardware/software selection component (suchas a load balancer).

With reference now to FIG. 6, in an illustrative example, assume thatthe DNS server component 124 has selected the resource cache component126 of POP 122. Upon receipt of the IP address for the resource cachecomponent 126, the client computing device 102 transmits a request forthe requested content to the resource cache component 126. The resourcecache component 126 processes the request in a manner described aboveand the requested content is transmitted to the client computing device102.

With reference now to FIG. 7, one embodiment of a request routine 700implemented by the CDN service provider 106 for processing a resourcerequest will be described. One skilled in the relevant art willappreciate that actions/steps outlined for routine 700 may beimplemented by one or many computing devices/components that areassociated with the CDN service provider 106. Accordingly, routine 700has been logically associated as being generally performed by the CDNservice provider 106, and thus the following illustrative embodimentsshould not be construed as limiting.

At block 702, one of the DNS server components 118, 124, 130 receives aDNS query corresponding to a resource identifier. As previouslydiscussed, the resource identifier can be a URL that has been embeddedin content requested by the client computing device 102 and previouslyprovided by the content provider 104. Alternatively, the resourceidentifier can also correspond to a CNAME provided by a content providerDNS server in response to a DNS query previously received from theclient computing device 102. The receiving DNS server also obtains an IPaddress associated with the DNS query from the requesting clientcomputing device 102 (“query IP address”) at block 702. The query IPaddress can correspond to an IP address of the client computing deviceor any local DNS resolver component associated with the client computingdevice.

Next, at block 704, the receiving DNS server obtains a location-basedidentifier associated with the query IP address. Each DNS servermaintains (or otherwise has access to) a data store 134 mapping a set oflocation-based identifiers with at least portions of known IP addresses(e.g., mapping a specific location-based identifier with a specific IPaddress or specific partial IP address). Utilizing the data store 134,the receiving DNS server attempts to match the IP address associatedwith the client computing device 102 DNS query (as transmitted via thelocal DNS resolver component) with the IP addresses in the data store134. If the query IP address can be partially matched to an IP addressin the data store 134, the DNS server identifies a correspondinglocation-based identifier. As similarly set forth above, thelocation-based identifiers can correspond to locations directlydetermined based on physical locations or logical locations associatedwith the origin of the DNS query. Additionally, the location-basedidentifier can be inferred based on associating a relative location toknown locations. For example, the location-based identifier can beattributed to known locations of POPs (corresponding to the CDN serviceprovider) based on measured latency information associated with requestrouting between the client computing device or its local DNS resolverand these POPs. The measured latency information can be premeasured,such as through testing procedures or previously observed requestrouting behavior. Alternatively, the measured latency information can bedynamically measured in a real time basis or semi-real time basis.

In an illustrative embodiment, the DNS server also optionally obtains aconfidence factor associated with the location-based identifier from thedata store 134 at block 704. The confidence factor corresponds to adegree of confidence in the accuracy of the associated location-basedidentifier to the query IP address. The optional confidence factor willbe further discussed in reference to FIG. 8.

Next, at a block 706, the receiving DNS server determines a POP from aset of one or more POPs associated with the obtained location-basedidentifier for resolving the resource request. Generally, the set of oneor more POPs are capable of servicing resource requests from a regionassociated with the identified location of the requesting clientcomputing device 102. As will be described further below, FIG. 8illustrates one embodiment of a request routing subroutine forperforming the functionality associated with block 706.

At decision block 708, a test is conducted to determine whether thecurrent DNS server is authoritative to resolve the DNS query. In oneillustrative embodiment, the DNS server can determine whether it isauthoritative to resolve the DNS query if the determined POP forresolving the resource request corresponds to the same POP associatedwith the receiving DNS server. If the determined POP indeed correspondsto the same POP associated with the receiving DNS server, then thereceiving DNS server is considered to be authoritative, and thereceiving DNS server identifies a cache server associated with theresource cache component from the same POP to process a subsequentclient resource request (e.g., a request for the embedded resource) atblock 710. The receiving DNS server resolves the DNS query by returningthe IP address of, for example, a default or specific cache server or aload balancing component (as appropriate) associated with the resourcecache component from the same POP. A number of methodologies forselecting an appropriate resource cache component at the POP may beimplemented.

Alternatively, if at decision block 708 the determined POP correspondsto another POP of the CDN service provider 106, and hence the receivingDNS server is not authoritative, the receiving DNS server selects andtransmits an alternative resource identifier at block 712. Specifically,in one embodiment, the receiving DNS server identifies an appropriateCNAME corresponding to the selected POP and transmits the CNAME to theclient computing device 102. At block 714, different DNS servercomponents 118, 124, 130 then receive a DNS query from the clientcomputing device 102 corresponding to the CNAME. The routine 700 thenreturns to decision block 708 and continues to repeat as appropriate.

Alternative or additional methodologies may also be practiced todetermine whether the DNS server is authoritative. In one embodiment,the receiving DNS server may maintain one or more CNAMEs that definevarious alternatives for request routing processing based on geographicregions of the CDN service provider 106. In this embodiment, instead ofdetermining a POP associated with the obtained location-based identifierat block 706, the receiving DNS server can determine a destinationidentifier associated with the obtained location of the client computingdevice, as will be similarly discussed below in reference to FIG. 8 atblock 806. The DNS server in this alternative embodiment can then selectan appropriate CNAME of an alternative POP based on the determineddestination identifier alone or in combination with other requestrouting criteria.

With reference now to FIG. 8, one embodiment of a request routingsubroutine 800 for selecting a POP associated with the location of therequesting client computing device will be described. One skilled in therelevant art will appreciate that actions/steps outlined for routine 800may be implemented by one or many computing devices/components that areassociated with the CDN service provider 106. Accordingly, routine 800has been logically associated as being performed by the CDN serviceprovider 106.

At decision block 802, where the receiving DNS server of the CDN serviceprovider 106 has obtained a confidence factor associated with thelocation-based identifier (from block 704 of FIG. 7), a test isperformed to determine whether the confidence factor exceeds a minimumthreshold value. If the confidence factor does not exceed a minimumthreshold, the DNS server assigns a default location-based identifier atblock 804. In one embodiment, the default location-based identifier maycorrespond to the location of the receiving DNS server. If theconfidence factor associated with the obtained location-based identifierexceeds the minimum threshold at block 802 or after a defaultlocation-based identifier is assigned at block 804, the receiving DNSserver determines a destination identifier for the DNS query at block806.

However, in an alternative embodiment, the foregoing functionalityassociated with obtaining and analyzing the confidence factor may beeliminated. In one embodiment, this functionality may instead beimplemented as a preprocessing step such that the query IP address tolocation-based identifier mappings provided in the data store 134already take a confidence assessment into consideration. For example,prior to generating the query IP address to location-based identifiermappings, any data mapping entry having a low confidence factor may befiltered out of the data mappings. The filtered query IP address tolocation-based identifier mappings may then be used by the CDN serviceprovider 106 to determine a destination identifier at block 806.

Returning to block 806 of FIG. 8, in one embodiment, the receiving DNSserver determines the destination identifier according to a manuallygenerated table from the data store 134 in which the destinationidentifier is determined as a function of the location-based identifier.However, the receiving DNS server can also provide an alternativedestination identifier in accordance with a manually initiatedadministrative process. One embodiment of the selection of the initialdestination identifier and the manually initiated administrative processfollows.

In an illustrative embodiment, the receiving DNS server utilizes themanually generated table mapping location-based identifiers todestination identifiers based on vector mapping and additional CDNadministrator manipulation. The destination identifier corresponds to adefinition of a geographic region encompassing one or more locations(e.g., a West Coast destination encompassing the states of Washington,Oregon and California). However, the DNS server may be configured tooverride the default destination identifier in accordance with amanually configured exception process determined as a function of theidentity of the content provider (as obtained through the contentprovider identifier included in the DNS query).

In one embodiment, a CDN administrator can override the allocation of adestination identifier for specific content provider identifiers. Forexample, the DNS server can utilize the content provider identifier toensure that the content provider's subscription with CDN serviceprovider 106 allows content to be served from the destination identifiedin the mapping table. As another example, the content provideridentifier can be manually designated to be associated with analternative destination identifier to redistribute at least a portion ofincoming resource requests for a particular content provider amongseveral POPs (e.g., to avoid servicing content requests for a single webpage via a single destination by offloading to a different destination).

Next, at block 808, based on the selected destination identifier, thereceiving DNS server selects a POP from a list of one or more POPs thathave been manually determined by the CDN administrator to be capable ofservicing resource requests for the identified destination. If more thanone POP is identified in the list of POPS, the receiving DNS server canselect a specific POP according a specified distribution allocation forthe corresponding destination (e.g., POP A (75%); POP B (25%)).

The receiving DNS server then determines whether the selected POP isavailable at decision block 810. In one embodiment, the DNS serverevaluates the availability of the selected POP using POP healthinformation indicative of the availability of the selected POP toprocess incoming resource requests. If the selected POP is available (asindicated via the POP health information), the receiving DNS servermaintains the POP selection from block 808. Accordingly, the processwill return to decision block 708 of FIG. 7, where if the receiving DNSserver is not authoritative, the receiving DNS server returns a CNAMEthat will result in the receipt of the DNS query by the selected POP (orone of a set of identified POPs). If, however, the selected POPcorresponds to the current POP of the receiving DNS server (i.e., thereceiving DNS server is authoritative), the receiving DNS serverresolves the DNS query by returning the IP address of the defaultresource cache component at the POP as the CNAME does not necessarilyneed to be provided (unless additional request routing processing willbe implemented).

If the selected POP is not available (as indicated via the POP healthinformation), the receiving DNS server can select an alternative POP atblock 814 to process the DNS query. In one embodiment, the alternativePOP can be selected via a failover list of alternative POPs that ismanually set by a CDN administrator. Specifically, the receiving DNSserver can select a specific alternative POP from the failover listaccording to a specified distribution. As similarly described above,processing will then return to decision block 708 of FIG. 7, where ifthe receiving DNS server is not authoritative for the alternative POP,the receiving DNS server returns a CNAME that will result in the receiptof the DNS query by the selected alternative POP (or one of a set ofPOPs). If, however, the selected alternative POP corresponds to thecurrent POP of the receiving DNS server (i.e., the receiving DNS serveris authoritative), the receiving DNS server resolves the DNS query byreturning the IP address of the default resource cache component at thealternative POP as the CNAME does not necessarily need to be provided(unless additional request routing processing will be implemented).

It will be appreciated by those skilled in the art and others that allof the functions described in this disclosure may be embodied insoftware executed by one or more processors of the disclosed componentsand mobile communication devices. The software may be persistentlystored in any type of non-volatile storage.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment.

Any process descriptions, elements, or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved, as would be understood by those skilled in the art. It willfurther be appreciated that the data and/or components described abovemay be stored on a computer-readable medium and loaded into memory ofthe computing device using a drive mechanism associated with a computerreadable storing the computer executable components such as a CD-ROM,DVD-ROM, or network interface further, the component and/or data can beincluded in a single device or distributed in any manner. Accordingly,general purpose computing devices may be configured to implement theprocesses, algorithms and methodology of the present disclosure with theprocessing and/or execution of the various data and/or componentsdescribed above.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which are to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

1. A method comprising: obtaining a DNS query from a client computingdevice at a first DNS server, wherein the DNS query corresponds to arequested resource associated with an original resource identifierprovided by a content provider and wherein the first DNS servercorresponds to a content delivery network service; obtaining a query IPaddress associated with the DNS query at the first DNS server; obtaininga location-based identifier associated with the query IP address and aconfidence factor, the confidence factor corresponding to a degree ofconfidence associated with the accuracy of the location-based identifierto query IP address association; determining whether the confidencefactor exceeds a threshold value; if the confidence factor exceeds thethreshold value: determining a destination identifier associated withthe DNS query, wherein the destination identifier is determined based onthe location-based identifier; selecting a network point of presenceassociated with the content delivery network service provider based onthe destination identifier; determining whether the first DNS server isauthoritative to the DNS query based on the selected network point ofpresence; and if the first DNS server is not authoritative: obtaining analternative resource identifier based on the selected network point ofpresence, wherein the alternative resource identifier includesinformation for causing a DNS query to resolve to a domain correspondingto the selected network point of presence; transmitting the alternativeresource identifier to the client computing device; obtaining asubsequent DNS query from the client computing device at a second DNSserver, wherein the subsequent DNS query corresponds to the alternativeresource identifier provided by the content delivery network serviceprovider; determining whether the second DNS server is authoritative tothe subsequent DNS query; selecting a cache component for providingcontent associated with the original resource request if the second DNSserver is authoritative to the second DNS query; and transmittinginformation identifying the selected cache component if the second DNSserver is determined to be authoritative.
 2. The method as recited inclaim 1 further comprising assigning a location-based identifierassociated with the first DNS server if the confidence factor does notexceed the threshold value.
 3. The method as recited in claim 1, whereinthe destination identifier corresponds to a geographic regionencompassing a location associated with the location-based identifier.4. The method as recited in claim 1 further comprising overriding thedetermined destination identifier based on the original resourceidentifier, wherein the original resource identifier providesinformation associated with an alternative destination identifier. 5.The method as recited in claim 1, wherein selecting a network point ofpresence comprises selecting a network point of presence from a set ofnetwork points of presence capable of servicing resource requestsassociated with the determined destination identifier.
 6. The method asrecited in claim 5, wherein the network point of presence is selectedfrom the set of network points of presence based on a distributionallocation.
 7. The method as recited in claim 1 further comprising:determining whether the selected network point of presence is availableprior to determining whether the first DNS server is authoritative tothe DNS query based on the selected network point of presence; if theselected network point of presence is available, maintaining theselected network point of presence; and if the selected network point ofpresence is not available, selecting an alternative network point ofpresence.
 8. The method as recited in claim 7, wherein the availabilityof the selected network point of presence is based on health informationindicative of the availability of the selected network point of presenceto process incoming resource requests.
 9. The method as recited in claim7, wherein selecting an alternative network point of presence comprisesselecting an alternative network point of presence from a failover listof alternative network points of presence.
 10. The method as recited inclaim 9, wherein the alternative network point of presence is selectedfrom the failover list based on a distribution allocation.
 11. Themethod as recited in claim 1 further comprising: if the first DNS serveris determined to be authoritative: selecting a cache component forproviding content associated with the original resource request; andtransmitting information identifying the selected cache component. 12.The method as recited in claim 1 further comprising overriding thedetermined destination identifier based on an identity of the contentprovider.
 13. The method as recited in claim 12, wherein the determineddestination identifier is overridden if the content provider'ssubscription with the content delivery network service provider does notprovide for content to be provided from a destination corresponding tothe destination identifier.
 14. The method as recited in claim 12,wherein the determined destination identifier is overridden if thecontent provider's subscription with the content delivery networkservice provider provides for use of an alternative destinationidentifier.
 15. The method as recited in claim 1, wherein the query IPaddress is associated with the client computing device.
 16. The methodas recited in claim 15, wherein the query IP address is associated witha DNS resolver component associated with the client computing device.17. The method as recited in claim 1, wherein the location-basedidentifier corresponds to a physical location associated with the clientcomputing device.
 18. The method as recited in claim 1, wherein thelocation-based identifier corresponds to a logical location associatedwith the client computing device.
 19. The method as recited in claim 1,wherein the location-based identifier corresponds to a relativelocation.
 20. The method as recited in claim 19, wherein the relativelocation is inferred based on an association of the relative location toa known location.
 21. The method as recited in claim 20, wherein therelative location is inferred based on latency information
 22. A methodcomprising: obtaining a DNS query from a client computing device at afirst DNS server, wherein the DNS query corresponds to a requestedresource associated with an original resource identifier provided by acontent provider and wherein the first DNS server corresponds to acontent delivery network service; obtaining a query IP addressassociated with the DNS query at the first DNS server; obtaining alocation-based identifier associated with the query IP address;selecting a network point of presence associated with the contentdelivery network service provider based on the location-basedidentifier; determining whether the first DNS server is authoritative tothe DNS query based on the selected network point of presence; and ifthe first DNS server is not authoritative: obtaining an alternativeresource identifier based on the selected network point of presence,wherein the alternative resource identifier includes information forcausing a DNS query to resolve to a domain corresponding to the selectednetwork point of presence; and transmitting the alternative resourceidentifier to the client computing device.
 23. The method as recited inclaim 22 further comprising determining a destination identifierassociated with the DNS query, wherein selecting a network point ofpresence is further based on the destination identifier.
 24. The methodas recited in claim 23, wherein the destination identifier is determinedas a function of the location-based identifier.
 25. The method asrecited in claim 24, wherein the destination identifier corresponds to ageographic region encompassing a location associated with thelocation-based identifier.
 26. The method as recited in claim 23 furthercomprising overriding the determined destination identifier based on anidentity of the content provider.
 27. The method as recited in claim 26,wherein the identity of the content provider is obtained based on theoriginal resource identifier.
 28. The method as recited in claim 26,wherein the determined destination identifier is overridden if thecontent provider's subscription with the content delivery networkservice provider does not provide for content to be provided from adestination corresponding to the destination identifier.
 29. The methodas recited in claim 26, wherein the determined destination identifier isoverridden if the content provider's subscription with the contentdelivery network service provider provides for use of an alternativedestination identifier.
 30. The method as recited in claim 23 furthercomprising overriding the determined destination identifier based on theoriginal resource identifier, wherein the original resource identifierprovides information associated with an alternative destinationidentifier.
 31. The method as recited in claim 23, wherein thedestination identifier is determined based on an identity of the contentprovider.
 32. The method as recited in claim 31, wherein the destinationidentifier is further determined based on the obtained location-basedidentifier.
 33. The method as recited in claim 23, wherein selecting anetwork point of presence comprises selecting a network point ofpresence from a set of network points of presence capable of servicingresource requests associated with the determined destination identifier.34. The method as recited in claim 33, wherein the network point ofpresence is selected from the set of network points of presence based ona distribution allocation.
 35. The method as recited in claim 22 furthercomprising: determining whether the selected network point of presenceis available prior to determining whether the first DNS server isauthoritative to the DNS query based on the selected network point ofpresence; if the selected network point of presence is available,maintaining the selected network point of presence; and if the selectednetwork point of presence is not available, selecting an alternativenetwork point of presence.
 36. The method as recited in claim 35,wherein the availability of the selected network point of presence isbased on health information indicative of the availability of theselected network point of presence to process incoming resourcerequests.
 37. The method as recited in claim 35, wherein selecting analternative network point of presence comprises selecting an alternativenetwork point of presence from a failover list of alternative networkpoints of presence.
 38. The method as recited in claim 37, wherein thealternative network point of presence is selected from the failover listbased on a distribution allocation.
 39. The method as recited in claim22 further comprising: if the first DNS server is determined to beauthoritative: selecting a cache component for providing contentassociated with the original resource request; and transmittinginformation identifying the selected cache component.
 40. The method asrecited in claim 22 further comprising obtaining a confidence factorcorresponding to a degree of confidence associated with the accuracy ofthe location-based identifier to query IP address association.
 41. Themethod as recited in claim 40, wherein a network point of presence isselected based on the location-based identifier if the confidence factorexceeds a threshold value.
 42. The method as recited in claim 22,wherein the location-based identifier is obtained from a data storecontaining query IP address to location-based identifier mappingentries.
 43. The method as recited in claim 42, wherein the data storecontains query IP address to location-based identifier mappings only forentries exceeding a minimum threshold confidence factor, the confidencefactor corresponding to a degree of confidence associated with theaccuracy of the location-based identifier to query IP addressassociation.
 44. The method as recited in claim 22, wherein the query IPaddress is associated with the client computing device.
 45. The methodas recited in claim 44, wherein the query IP address is associated witha DNS resolver component associated with the client computing device.46. The method as recited in claim 22, wherein the location-basedidentifier corresponds to a physical location associated with the clientcomputing device.
 47. The method as recited in claim 22, wherein thelocation-based identifier corresponds to a logical location associatedwith the client computing device.
 48. The method as recited in claim 22,wherein the location-based identifier corresponds to a relativelocation.
 49. The method as recited in claim 48, wherein the relativelocation is inferred based on an association of the relative location toa known location.
 50. The method as recited in claim 49, wherein therelative location is inferred based on latency information
 51. A systemfor request routing comprising: a first network point of presenceassociated with a content delivery network service provider, wherein thefirst network point of presence includes a DNS server component thatreceives a DNS query from a client computing device, wherein the DNSquery corresponds to a requested resource associated with a firstresource identifier, and wherein the DNS server in the first networkpoint of presence is operable to: obtain a query IP address associatedwith the DNS query at the first DNS server; obtain a location-basedidentifier associated with the query IP address; select a network pointof presence associated with the content delivery network serviceprovider based on the location-based identifier; determine whether thefirst DNS server is authoritative to the DNS query based on the selectednetwork point of presence; and if the first DNS server is notauthoritative: obtain an alternative resource identifier based on theselected network point of presence, wherein the alternative resourceidentifier includes information for causing a DNS query to resolve to adomain corresponding to the selected network point of presence; andtransmit the alternative resource identifier to the client computingdevice.
 52. The system as recited in claim 51, wherein the DNS server inthe first network point of presence is further operable to determine adestination identifier associated with the DNS query, wherein selectinga network point of presence is further based on the destinationidentifier.
 53. The system as recited in claim 52, wherein thedestination identifier is determined as a function of the location-basedidentifier.
 54. The system as recited in claim 52, wherein the DNSserver in the first network point of presence is further operable tooverride the determined destination identifier based on an identity ofthe content provider.
 55. The system as recited in claim 54, wherein theidentity of the content provider is obtained based on the originalresource identifier.
 56. The system as recited in claim 51, whereinselecting a network point of presence comprises selecting a networkpoint of presence from a set of network points of presence capable ofservicing resource requests associated with the determined destinationidentifier.
 57. The system as recited in claim 56, wherein the networkpoint of presence is selected from the set of network points of presencebased on a distribution allocation.
 58. The system as recited in claim51, wherein the DNS server in the first network point of presence isfurther operable to: determine whether the selected network point ofpresence is available prior to determining whether the first DNS serveris authoritative to the DNS query based on the selected network point ofpresence; maintain the selected network point of presence if theselected network point of presence is available; and select analternative network point of presence if the selected network point ofpresence is not available.
 59. The system as recited in claim 58,wherein the availability of the selected network point of presence isbased on health information indicative of the availability of theselected network point of presence to process incoming resourcerequests.
 60. The system as recited in claim 58, wherein selecting analternative network point of presence comprises selecting an alternativenetwork point of presence from a failover list of alternative networkpoints of presence.
 61. The system as recited in claim 60, wherein thealternative network point of presence is selected from the failover listbased on a distribution allocation.
 62. The system as recited in claim51 further comprising: a second network point of presence associatedwith a content delivery network service provider, wherein the secondnetwork point of presence includes a DNS server component that receivesa subsequent DNS query from a client computing device, wherein thesubsequent DNS query corresponds to a requested resource associated withthe alternative resource identifier, and wherein the DNS server in thesecond network point of presence is operable to: resolve the subsequentDNS query to identify a cache component for providing content associatedwith the original resource request; and transmit information identifyingthe identified cache component to the client computing device.
 63. Amethod comprising: obtaining a DNS query from a client computing deviceat a first DNS server, wherein the DNS query corresponds to a requestedresource associated with an original resource identifier provided by acontent provider and wherein the first DNS server corresponds to acontent delivery network service; obtaining a query IP addressassociated with the DNS query at the first DNS server; obtaining alocation-based identifier associated with the query IP address;obtaining a destination identifier based on the obtained location-basedidentifier; determining whether the first DNS server is authoritative tothe DNS query based on the destination identifier; and if the first DNSserver is not authoritative: obtaining an alternative resourceidentifier based on the selected network point of presence, wherein thealternative resource identifier includes information for causing a DNSquery to resolve to a domain corresponding to the selected network pointof presence; and transmitting the alternative resource identifier to theclient computing device.
 64. A method for request routing comprising:obtaining a DNS query from a client computing device at a first DNSserver, wherein the DNS query corresponds to a requested resourceassociated with a resource identifier and wherein the first DNS servercorresponds to a content delivery network service provider; determiningthat the first resource identifier is associated with an alternativeresource identifier based on location information associated with theclient computing device, wherein the location information is obtainedfrom information corresponding to a mapping of at least partial IPaddresses to known locations; transmitting the alternative resourceidentifier to the client computing device, wherein the alternativeresource identifier includes information for causing a DNS query toresolve to a domain corresponding to the content delivery serviceprovider and supplemental request routing information not included inthe first resource identifier; obtaining a subsequent DNS query from theclient computing device at a second DNS server, wherein the subsequentDNS query corresponds to the alternative resource identifier provided bythe content delivery network service provider and wherein the second DNSserver corresponds to the content delivery network service provider;resolving the subsequent DNS query, at the second DNS server, toidentify a cache component for providing content associated with theoriginal resource request; and transmitting information identifying theidentified cache component to the client computing device.